This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The rhesus CMV isolates, rhCMV68-1 and rhCMV180-92, show genetic diversity in the ULb'region which contains genes encoding cellular tropism genes. Experimental infection with both rhCMV68-1 and rhCMV180-92 successfully establishes persistent, asymptomatic infection in immunocompetent rhesus macaques and leads to CMV disease in SIV-infected macaques. In this project, the role of the ULb'genetic content in determining in vivo tissue tropism and spread of CMV is being investigated. Tissue distribution of CMV is being examined by immunohistochemical and PCR analysis. Heterogeneity in the genetic content of the ULb'region of virus recovered from saliva and tissues of experimentally rhCMV-infected macaques is also being evaluated by sequencing of recovered viral DNA.